The Pitot tube and manometer are used
for measuring low velocities of water in the flume. The manometer has
Paraffin/Kerosene above each column of water and if used with excessively high
velocities, the Paraffin will be pushed out of the manometer into the flexible
tubing which may result in Paraffin entering the flume.

REMEMBER: DO NOT open the valve at
the base of the reservoir on the manometer during operation.

Slowly open the flume inlet valve and
allow water to flow slowly through the flume. Carefully open the isolating
valves at the base of the manometer and note the difference in levels in the two
limbs of the manometer.

The velocity of the water is calculated
as follows:

For the Pitot
tube v =
Eqn 1

For the
manometer
Eqn 2

Where:

v = Local velocity of
water
(m/s)

k = Pitot tube coefficient (assumed to
be 1.0)

pt = Total
pressure
(N/m2)

ps = Static
pressure
(N/m2)

ρf
= Density operating fluid, water
(kg/m3)

ρm= Density of manometer fluid,
paraffin
(kg/m3)

h = Difference in levels in
manometer
(m)

g = Gravitational
constant
(9.81m/s)

By substituting Eqn 2 into Eqn
1:

v =

density of paraffin is 784 kg/m3

v =
(m/s)

For defining the position of the Pitot
tube relative to the flume, the following convention can be used:

xp = dist. along the
flume (scale marked on the side of flume)
(m)

yp = location
across flume
(m)

zp = height above bed
of flume (vertical level gauge)
(m)

These dimensions can be tabulated with
the other results obtained.

The Pitot tube assembly is used where
velocities are required. The velocity profile in the flume can be obtained by
moving the Pitot tube vertically and horizontally across the flume at different
sections, noting the readings on the manometer at each position and converting
these readings to a series of velocity profiles.